package asimes.didi;

/**
 * Created by Liangweiwei on 2016/9/18.
 */
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();
        int count = 0;
        for(int i=1;i<=N;i++){
            int j =i;
            while(j%5 ==0){
                count ++;
                j/=5;
            }
        }
        System.out.println(count);
    }
}